为什么将无符号整数转换为字节数组形式以“ 3”开头的字符串？

If I do the following in golang:

data := []byte{}
data = append(data, '1')
data = append(data, '2')

fmt.Printf("%d
", len(data))
fmt.Printf("%x
", fmt.Sprintf("%d", len(data)))

I get 2 and 32, respectively, instead of just 2 on both lines (obviously the array has only two elements).

If I do something similar-ish in solidity:

bytes memory encodedPack = abi.encodePacked(prefix, length, signedMessage)

The encodePacked function also prepends the length with 3 in the final byte array.

According to the ASCII table, 3 represents "end of text". Is this what this 3 is for?

Sprintf() returns a string. You are printing the string "2" which in ASCII is 0x32.

The 3 here is not end-of-text. If you look at the ASCII table, you will notice that the characters "0" to "9" are encoded as 0x30 until 0x39.